Conventional surface protective layers and interlayer insulating layers for semiconductor devices can include a polyimide resin, which can have excellent heat resistance and electrical characteristics, mechanical characteristics, and the like.
Polyimide resins have recently been used in the form of a photosensitive polyimide precursor composition to form a surface protective layer, an interlayer insulating layer, and the like. The photosensitive polyimide precursor composition can be coated on a semiconductor device, patterned by ultraviolet (UV) rays, developed, and heat imidized. In this manner, it is possible to significantly shorten a process for making a surface protective layer, an interlayer insulating layer, and the like, compared to processes that use conventional non-photosensitive polyimide precursor compositions.
Photosensitive polyimide precursor compositions can be a positive type, in which an exposed part is dissolved by development, or a negative type, in which the exposed part is cured and maintained. A positive type composition can be useful in many applications because it can be developed by a non-toxic alkali aqueous solution. Positive photosensitive polyimide precursor compositions can include a polyimide precursor of polyamic acid, a photosensitive material of diazonaphtoquinone, and the like. However, the positive photosensitive polyimide precursor composition may not provide a desired pattern because the carbonic acid of the polyamidic acid used can be too highly soluble in an alkali.
Japanese Patent Laid-Open Publication No. H10-307393 is directed to a material including a phenolic hydroxyl acid group instead of a carbonic acid which is introduced by esterificating polyamidic acid with an alcohol compound having at least one hydroxyl group. This material, however, may be insufficiently developed, which can cause problems such as reduced layer thickness (layer loss) or resin delamination from the substrate.
Recently, a material in which a polybenzoxazole precursor is mixed with a diazonaphtoquinone compound has drawn attention (Japanese Patent Laid-open Publication No. S63-96162). When the polybenzoxazole precursor composition is actually used, however, an unexposed part can exhibit significant layer loss, so it can be difficult to obtain a desirable pattern after the developing process. Increasing the molecular weight of the polybenzoxazole precursor may reduce layer loss of the unexposed part but can generate development residue (scum), which can deteriorate resolution and increase development times on the exposed part.
In order to solve this problem, it has been reported that layer loss can be suppressed by adding a certain phenol compound to a polybenzoxazole precursor composition (Japanese Patent Laid-Open Publication No. H9-302221 and Japanese Patent Laid-Open Publication No. 2000-292913). However, the effect of suppressing layer loss of the unexposed part may be insufficient. Accordingly, there is still a need to improve layer loss suppression and to prevent development residue (scum) generation.
After forming the pattern, the conventional photosensitive polyimide or polybenzoxazole is cured at a temperature of around 350° C. Magnetoresistive RAM (MRAM) that is usable for the next generation memory device is weak at a high temperature, so devices for the same require a low curing process temperature. Accordingly, such devices need a material that can be used as a surface protective layer and an interlayer insulating layer and that can be cured at a low temperature of 260° C. or below.
By using a latent thermal acid generator or a monomer having excellent flexibility, it has been reported that it is possible to use low curing temperatures by using a polymerized polybenzoxazole precursor (Japanese Patent Laid-Open Publication No. 2006-349700 and Japanese Patent Laid-Open Publication No. 2007-079264). However, the obtained polybenzoxazole precursor has poor adherence to the substrate. Accordingly, there is still a need to improve the various characteristics of a layer including the same.